As the electronic and electric appliances are reduced in size recently, component parts are also reduced in size and advanced in definition, and high definition and high precision are demanded in machining of parts at machining precision of ±50 μm or less. In the conventional press processing or blanking process, the precision is about ±100 μm at most, and such demand cannot be satisfied. Drilling of materials is also demanded to conform to high definition and high precision, and drilling by using conventional drill or die cannot meet the needs.
As the solving method, recently, processing methods of various materials by using a laser beam have been gaining attention. Examples of such a technology include a method of dicing a workpiece by a laser beam by supporting and fixing the workpiece on a dicing sheet (Japanese Patent Application Laid-Open No. 2002-343747). The dicing sheet disclosed therein includes a base material having a support sheet, and an adhesive layer disposed on one side of the base material, where the adhesive layer can be cut off by the laser beam, and the support sheet cannot be cut off by the laser beam.
Another proposed method is to dice a semiconductor wafer by combining a laser with a water microjet (Japanese Patent Application Laid-Open No. 2003-34780). As a proposed adhesive tape for laser dicing proposed therein, a non-radiation curing type adhesive layer and a radiation curing type adhesive layer are formed on one side of the base material, where the base material is transmissive of a jet stream of the water jet, and the non-radiation curing type adhesive layer is disposed between the base material and radiation curing type adhesive layer.
When a laser beam is used, however, decomposition products of carbon and others generated from the workpiece, adhesive tape and a adsorption board at the time of laser processing deposit on the surface of the workpiece, and postprocessing called desmearing is needed for removing them. Adhesion strength of the decomposition products becomes stronger in proportion to the power of the laser beam, and when the laser beam power is increased, it tends to be difficult to remove the decomposition products in postprocessing. Accordingly, a problem has been noted that an improvement of processing throughput by increasing the laser power may be hindered, or processing precision may be lowered. Moreover, if the dicing sheet is also cut off when cutting the workpiece, the laser processed part drops off. Therefore, there is also a problem that a certain portion must be kept uncut when cutting, which makes the handling performance poor.
When using the dicing sheet disclosed in Japanese Patent Application Laid-Open No. 2002-343747, the adhesive layer is thermally cut off by the fundamental wave of YAG laser (wavelength 1064 nm) or a laser beam of ruby laser (wavelength 694 nm), and decomposition products of an adhesive layer may invade into the interface between the dicing sheet and the workpiece, and may stick stubbornly to the interface area. As a result, there is a problem that it is hard to remove the dicing sheet from the workpiece after laser processing, or laser-processing precision is lowered.
In the case of the adhesive tape disclosed in Japanese Patent Application Laid-Open No. 2003-34780, when the water microjet and the laser are combined and used in dicing of semiconductor wafer, thermal damage of adhesive tape is decreased by cooling effect of water jet, and it may be expected to suppress dissolving or decomposing of the adhesive layer or the base material due to heat by laser irradiation. However, when the adhesive tape is applied in a method of dicing a semiconductor wafer by using only a laser, due to the heat by the laser irradiation, the adhesive layer or base material may be dissolved, and decomposition products of the adhesive layer and the base material may invade into the interface between the adhesive sheet and the semiconductor wafer, sticking stubbornly to the interface area, and similar problems may occur. Further, when water microjet is used, there is a limit in reducing the cutting width since the cutting width in dicing is defined by the diameter of the water jet, and thus it is inferior in the aspect of manufacturing efficiency of semiconductor chip.